The present invention generally relates to torque measurement, and more particularly to a method of using a magnetic fluid clutch for torque measurement as well as to a combined torque measurement and clutch apparatus for use with this method.
Engines which are utilized in single-engine helicopter applications typically incorporate a freewheeling clutch and a separate torque measuring device which is within or attached to the reduction gear box, or is attached to a drive system of the helicopter in order to establish torque transmission to the main rotor and to monitor the torque value transmitted to the main rotor, or facilitate auto-rotation in the event of a reduction or loss of engine power.
It is known that torque measurement can be achieved by a phase shift measuring device used to measure an angular deviation between two ends of a rotating shaft which transmits torque. One example of such a phase shift measuring device is described in U.S. Pat. No. 4,520,681, issued to Moore et al. on Jun. 4, 1985. The device of Moore et al. includes two slotted disks disposed on a rotating shaft a predetermined distance apart. A slot is formed in the periphery of each of the disks. A light source and a light sensor are mounted stationary with respect to the shaft and proximate to the periphery of each disk. The time duration between signals from the respective sensors is measured and the angular deviation of the two disks can be calculated therefrom. Measurement of this angular deviation determines the amount of twist on the shaft portion between the two disks. The torque can then be calculated from this angle of twist, by a computerized central processing device.
Another example of phase shift measuring devices is described in U.S. Pat. No. 5,918,286, which issued to Smith et al. on Jun. 29, 1999. Smith et al. describe a device for torque measurement of rotating shafts for the purpose of calculating the shaft power without using sensors mounted or glued to the shaft. Accuracy is increased by using only one single optical electronic sensor in the pulse receiver. The light is transmitted from the source/transmitter through optical fiber. The light beam is pulsed within two air gaps by coding disks/gear wheels mounted to the shaft at a convenient distance from each other. The time displacement between the vanes/teeth on the two disks/gear wheels is a measure on the shaft torque, enabling the shaft power to be calculated by a computer. To increase the accuracy in case of shaft vibration, the width modulated pulses are accumulated and averaged at convenient numbers of shaft turns. The accuracy is increased by detecting both rising and falling pulse edges in order to double the number of pulses of each shaft turn.
The angular deviation of the rotating shaft which transmits torque depends on both the torque value being transmitted through the rotating shaft and the resilient property in angle deviation of the rotating shaft, which is inherent in the nature of the shaft material and is further determined by the geometry of the shaft. Thus, the amount of torque transmitted through the rotating shaft can be calculated from the angular deviation of the rotating shaft because the geometry of the rotating shaft and the nature of the shaft material are not variable. Nevertheless, the rotating shaft is generally designed for full load torque transmission and therefore the angular deviation of the rotating shaft at a low torque level will be relatively small, resulting in inaccuracies in the torque measurement. However, such accuracy is needed for example, in helicopter rotor applications.
Therefore, there is a need for a method and apparatus for torque measurement which provide adequate measuring accuracy at various torque levels.
A primary object of the present invention is to provide a method of using a magnetic fluid clutch for torque measurement and transmission.
Another object of the present invention is to provide a method and apparatus for torque measurement which provides adequate accuracy at various torque levels.
A further object of the present invention is to provide a combined torque measurement and clutch apparatus and a method for using the apparatus for torque transmission and torque measurement.
The present invention is generally directed to a method of using a magnetic fluid clutch for torque measurement. The method comprises: modulating electric current through a coil of the magnetic fluid clutch to maintain a steady-state quasi-solid phase of a magnetic fluid medium contained within the magnetic fluid clutch when the magnetic fluid clutch is clutched to transmit torque from a torque input end of the clutch to a torque output end of the clutch, thereby ensuring that the torque output end rotates in response to the rotation of the torque input end without relative rotational slippage therebetween; and measuring a deflection value associated with the magnetic fluid clutch.
The deflection value associated with the magnetic fluid clutch is preferably measured by way of a phase shift measurement between the torque input end and the torque output end of the magnetic fluid clutch. The deflection value associated with the magnetic fluid clutch is also preferably measured by way of distortion measurement of a magnetic field applied to the magnetic fluid medium and then, a torque value can be calculated from the measured deflection value associated with the magnetic fluid clutch.
The viscosity/solidity of the magnetic fluid medium which is maintained in the steady-state quasi-solid phase, according to one embodiment of the present invention, can be varied to a level which matches a level of torque being transmitted through the magnetic fluid clutch so that the deflection value being measured is optimized within an adequate measuring range of a measuring device used for the measurement. For example, electric current through the coil of the magnetic fluid clutch can be modulated to increase the viscosity/solidity of the magnetic fluid medium when the level of torque being transmitted is relatively large; and the electric current through the coil of the magnetic fluid clutch can be modulated to decrease the viscosity/solidity of the magnetic fluid medium when the level of torque being transmitted is relatively small. Nevertheless, the change of the viscosity/solidity of the magnetic fluid medium should not change the no slippage work condition of the magnetic fluid clutch when the magnetic fluid clutch is used for torque measurement.
In accordance with another aspect of the present invention, an apparatus is provided including a magnetic fluid clutch which has a torque input end and a torque output end. The magnetic fluid clutch further includes a magnetic fluid medium therein and a coil for generating a magnetic field and applying the magnetic field to the magnetic fluid medium. The torque input end is adapted to be connected to a torque supply source, an engine of a helicopter for example, and the torque output end is adapted to be connected to a rotational work device, the main rotor of the helicopter for example. The apparatus further includes a first detector positioned at the torque input end and a second detector positioned at the torque output end. A processor is provided for controlling current through the coil of the magnetic fluid clutch and for processing signals from the first and second detectors to calculate an angular deviation between the torque input end and the torque output end.
The processor is preferably incorporated into a controller of an engine, or incorporated into a controller of an aircraft.
In one embodiment of the present invention, the magnetic fluid clutch comprises a rotating shaft having a first end and a second end. One of the ends forms the torque output end of the magnetic fluid clutch. A casing surrounding the rotating shaft is rotatable relative to the rotating shaft, and contains the magnetic fluid medium therein. The rotating casing forms the torque input end of the magnetic fluid clutch. Rotating members such as blades are affixed to the respective rotating shaft and the inside surface of the casing in order to increase the frictional contact of the respective rotating shaft and the rotating casing with the magnetic fluid medium.
In another embodiment of the present invention, the magnetic fluid clutch comprises a stationary casing containing the magnetic fluid medium therein. A first rotating shaft and a second rotating shaft form the respective torque input end and torque output end. The respective rotating shafts extend oppositely and outwardly from the inside of the casing and are rotatable relative to each other and relative to the casing. A first plate and a second plate are affixed to the first and second rotating shafts respectively, and are axially spaced apart. The first plate and second plate are disposed in the magnetic fluid medium so that torque can be transmitted from the first plate to the second plate through the magnetic fluid medium when the viscosity/solidity of the magnetic fluid medium reaches a certain level.
The apparatus according to the present invention combines a clutch device with a torque measurement device and can have broad application potential, because of not only providing a new option for machine structure design, but also providing a new torque measurement method which provides more measurement accuracy. The latter is advantageous, particularly at low torque levels compared to a full load torque level of the machine into which the apparatus is incorporated.
Other advantages and features of the present invention will be better understood with reference to preferred embodiments of the present invention described hereinafter.